Radio compass



March 10, 1942. A. H. LAMB RADIO COMPASS Filed Oct. 23. 1939 2 Sheets-Sheet 1 March 10, 1942. A. H. LAMB 2,276,235

RADIO COMPASS Filed- Oct. 23, 1939 2 Sheets-Sheet 2 Patented Mar. 10, 1942 UNETE@ S'A'EE ?ATENT OFFECE RADIO COMPASS Application October 23, 1939, Serial No. 3005354 (Cl. 259-1D Weston Electrical 2 Ciaims.

This invention relates to radio compasses for use on marine vessels and aircraft, and particularly to a compass system including apparatus for automatically maintairing the directional antenna oriented on the selected radio transmitting station.

Various radio compass systems have been devised for indicating the direction to a radio transmitter by the Variations in phase or magnitude of signals received on drectional and nondirectional antennas as the directional antenna is manually rotated. It has also been proposed to rotate the directional antenna through relay systems that are brought into operation when the directional antenna or loop moves out of the plane to the transmtter, but vibration on vessels and aircraft makes it difficult to effect stable operation of relay circuits in response to the displacement of the sensitive instrument relay. The problem of obtaining a stable control of the position of the directional antenna or loop on aircraft is particularly difficult in view of the Vibration and the exacting design requirements of small size, light weight, and rapid response to "off course indications.

An object of this invention is to provide a radio compass including relay apparatus of high reliability for controlling the orientation of the directional antenna element and/or an indicating device. An object is to provide a radio compass system including a reversible motor for rotating the directional antenna, circuits for combining the signal Components received on a directional and a non-directional antenna to produce a Voltage indicative of the displacement of the loop from aplane that passes through the radio transmitter, and stable relay apparatus for controlling the motor operation in accordance with the magnitude of the produced voltage. Another object is to provide relay circuits that include grid glow tubes and that function properly in spite of vibration of the apparatus carrying the relay circuits. A further object is to prot Fig. 1 is a circuit diagram of a radio compass embodying the invention;

Figs. 2 and 3 are simplified diagrams of the circuits of one tube of the Fig. 1 circuit and of a modification, respectively;

Fig. 4 is a fragmentary elevation of one form of flexible vibratory Contacts for the instrument relay;

Fig. 5 is a curve sheet showing the relation between motor speed and the magnitude of the departure of the loop orientation from the position of balance;

Fig. 6 is a circuit diagram of another embodiment of the invention; and

Fig. '7 is a fragmentary circuit diagram of a modification of th Fig. 6 arrangement.

In Figs. 1 and 6 of the drawings, the antenna system includes a balanced loop or directional antenna l that is tunable by a condenser 2, and a non-directional or rod antenna 3. An audio frequency oscillator 4 supplies current to the loop through a transformer 5 and leads 6, and the combined outputs of the loops and local oscillator work into a balanced modulator l. The outputs of the modulator 'I and the non-directional antenna 3, after amplification by tubes 8, 9 respectively, are combined in a circuit l that works into an amplifier and detector ll.

The summation of the signal pick-up from the balanced loop and the rod antenna, when properly adjusted, results in a cardioid curve with reference to total signal versus orientation of the loop with respect to the transmitter when plotted in polar coordinates. This cardioid shaped response curve is modulated by the local oscillator 4 and the output from the amplifierdetector ll is therefore a current of the audio oscillator frequency that varies in phase and magnitude in accordance with the cardioid law With reference to the orientation of the loop antenna.

In the embodment illustrated in Fig. 1, the output from the amplifier-detector ll is fed to one co'il !2 of a dynamometer type measuring instrument relay that has a second winding |3 connected across a secondary winding [4 of the transformer '5. The pointer or contact arm |5 of the instrument relay is displaced in opposite directions `from an electrical zero position corresponding to "on course" orientation of the loop antenna l as the plane of the loop moves to the right or the left of the plane from the loop to a radio transmitter. Contacts !6, s' are located in fixed or relatively fixed positions at opposite sides of the electrical zero position to close relay circuits selectively in accordance with the dis placement of the contact arm. These relay cirthat are` connected between ground and the posiv tive terminal of a current source, such as the 12 volt storage battery in common use on aircraft. The control grid of tube ll is connected to ground through a pair of serially connected resistors l9,

20. The junction of the resistors is connected to the instrument relay contact IE by a lead 21, and

the plate of tube Il is connected throughthe motor field coil 22, motor armature 23 and lead 24 to a terminal of an alternating current source 25 that is preferably a vibratory invertor work-' ing out of the battery !8. The other output terminal is grounded, as shown, or may be returned to the negative terminal of battery !8. The instrument contact arm' is connected to the positive terminal of the battery !8 by a lead 26, and the cathode of tube ll is returned to the positive terminal of the heater element. A resistor 2'! or equivalent means is connected between the plate and cathode of tube ll to limit back e. m. f. and other transients that would render the tube l'l conductive during half-cycles When the plate potential isnegative with respect to the cathode. The circuits of the tube l'i" are symmetrical with those of tube H and the various elements are identified by the corresponding primed numerals but will not be described in detail.

The motor shaft 29 is connected'through gearing 30 to the staff 3! that carries the loop antenna l and has slip rings 32 for connecting the loop to the tuning condenser 2. Gearing 33 at the other end of the motor shaft 29 drives the flexible shaft 34 that actuates a compass or direction indicating instrument 35. 1

As will be apparent from the fragmentary circuit diagram, Fig. 2, the grids of the grid glow tubes are normally at a direct current potential that is negative with respect to the cathodes, the grids being returned to ground through resistors !9, while the cathodes are connected to the positive terminal of the battery !8. This negative bias which blocks plate current flow is removed when the instrument relay contacts !5, IS or !5, IS' close to connect the grid `of tube ll or ll', respectively, to the positive battery terminal through resistor IQ and lead 2 i or resistor l9' and lead 21'. Plate current flows during half-cycles of the alternating current from source that make the plates positive with respect to the cathodes so long as the instrument relay contacts are closed, but this half-cycle conductivity ceases as soon as the relay contacts open.

The operation of the radio compass system of Fig. 1 is therefo'e as follows. As is understood in the art, the audio frequency current delivered to the instrument winding !2 is of a magnitude and phase, with respect to the audio frequency input to the instrument winding l3 from the transformer seconda'y 14, that depends upon the orientation of the loop I with respect to the transmitter, and the instrument deflection is zero or a maximum when the loop is in the plane of the transmitter., Proper'orentation of the loop reduces the instrument relay deflection to zero, thus opening the relay contacts to render tubes I'I, ll non-conductive. *Movement of the vessel shown in Fig. 3, to bring the motor into operation by blocking plate current flow in one of the two tubes IT, IT' which, in the balanced loop condition, both pass current. The circuit connections difier from those of Figs. 1 and 2 in that the resistors !9, 20 are not conductively connected under normal conditions but are connected, respectively, to the contact !E and contact arm l5 ofvthe instrument relay. A condenser 36 may be shunted across the contacts !5, Hi, when a time delay is desired; and it is to be understood that the circuit connections to the tube l'l' are symmetrical with those of tube ll.

It will be apparent that, when the Fig. 3 circuit connections are substituted in the compass system of Fig. 1, a further change must be made in the connections to the ,winding of the instrument relay or in the motor circuit to efiect a rotation of the loop'l in the proper direction to restore the balanced condition. `'The armature of the motor is held stationary by equal currents in the two field windings 22, 22' so long as the instrument contact arm !5 remains out of engagement with the contacts IG, IB'. Departure of loop I from its desired orientation results in a current flow in the instrument coil !2 that deflects the contact arm !5 into engagement with one of the fixed contacts, for example the contact !6. The contact closure completes a conductive circuit from the grid of tube l'l to the negative terminal of the battery !8 and places a heavy negative bias on the grid. The tube l' is thus blocked and the motor is energized as the current through the field winding 22 is interrupted. This type of motor control has the ad-' Vantage that overrunning or hunting is precluded as tube I'I becomes conductive as soon as the instrument contact arm !5 leaves the contact l6. The balanced current flow through the opposed field windings 22, 22' acts as an electrical brake that quickly arrests the rotation of the motor armature.

The contact system of the instrument relay is an important feature of the invention as it provides -an .automatic control of the motor speed as a function ,of the displacement of the loop from its balance plane. As shown in Fig. 4, the contact arm l and contacts as, 16' are highly flexible and of such length that their free ends or contact portions are continuously vibrating. The contact members may be formed of fine springy wires or ribbons and, where space is not available for long contact members, a part !5' of the Wire or ribbon may be loosely coiled to encourage continuous Vibration. The spring contacts are always in relative motion, although this motion may be too small. to `be apparent to the naked eye, and tend to keep clean at the points of contact. The dirt particles and films'that caused trouble With prior contacts create 'little or no diffic`ulty with the freely vibrating 'contacts as the fluttering of the contacts gives, rise to an appreciable impact in spite of the 'low pressure that can be developed by an instrument type relay.

A substantial deflection of the relay contact arm 15, corresponding to a considerable offcourse condition, results in an average conta-ct pressure that maintains the contacts in continuous or almost continuous engagement in spite of the vibration of the spring contacts. The contacts vibrate apart during a considerable part of the time as the moving system of the relay approaches its zero position and the power supplied to the motor thus varies with the departure of the loop l from its on-course position. The relative duration of the open and closed condition of the contacts for different degrees of displacement of the loop l from on-course position is indicated graphically in Fig. .by widths of the hatched areas and the adjacent spaces, and the curve A shows the relation between motor speed and off-course position that results from the current pulses of different duration that are thus supplied to the motor.

The invention may be incorporated in radio compass systems, as described and claimed in the application of John H. Miller, Ser. No. 289,'703, Radio compass, filed Aug. 11, 1939, in which a rectifier bridge and direct current instrument relay are used in place of the less sensitive dynamometer type of relay. In one such adaptation of the invention, as shown in Fig. 6, the radio circuits are or may be substantially identical with those of Fig. 1 and the several parts are identified by corresponding reference numerals but will not be described in detail.

The audio output from the amplier-detector li is ed to the .primary of a transformer 38 that has a center tapped secondary connected across opposite terminals of a rectifier bridge 39. The small Copper oxide rectifiers 40 are arranged in "series aiding relation in the several bridge arms and a small resistance and sliding tap connection 4! may be provided at one terminal point for balancing the bridge. The secondary winding M' of transformer 5 of the audio oscllator system is also center tapped and is connected across the other pair of opposed terminals of the rectifier bridge. The moving coil cz of a sensitive direct current instrument relay is connected between the center taps of the winding and the secondary of transformer 38.

The contact arm 43 of the relay is grounded and the contacts 44, M' are connected to the control grids of tubes I'I, H', respectively, through resis-tors [9, 2@ and 19', 20'. The grids are fioating when the relay contacts are open and both tubes thus pass current to the motor field windings 22, 22' to prevent rotation of the motor so long -as the loop l is on course. As explained in the Miller application, the deviation of the relay contact arm 43 from a center Zero position is a function of the magnitude and phase relations of the two alternating current Components impressed upon the rectifier bridge, and the direction and extent of the contact arm displacement therefore varies with the direction and the extent of the movement of the loop I away from its desired on-course position. The motor is thereby energized to rotate the loop in the proper direction to restore a balanced condition when contact arm 43 engages contact 44 or 44' to block conduction through the associated tube by applying a negative bias. The motor speed varies with the departure of the loop from its balance position when the relay is provided with vibratory contacts.

A Simpler arrangement, as shown in the fragmentary circuit diagram of Fig. 7, includes the radio receiver and local oscillator of the Fig. 6 system but, for Simplicity, only the output windings of these parts have been illustrated. The control grids of tubes ll, ll" are connected by leads 45, 45' directly to the center taps of the secondary of transformer 33 and of winding M', respectively, and the grids are returned to the positive terminal of the battery 18 through 'the resistors 46, 46', respectively. The grid resistors thus complete a direct current output circuit for the rectifier bridge, and the bias voltages applied to the two grids vary in opposite sense when the balance condition of the bridge is disturbed by movement of the loop I from its on-course position. Both tubes are normally conductive and pass current to the opposed field windngs 22, 22' of the reversible motor. These field currents are equal and block operation of the motor so long as the rectifier bridge is balanced, but current flow in the direct current output circuit of the bridge establishes potentials across the resistors 45, 45' that increase the bas on one tube and decrease that on the other tube. Conducton through one tube is blocked when the grid bias falls below a critical value, and the motor then rotates in the direction determined by the other tube and its associated field winding to restore the loop l to its on-course position.

It is to be understood that the invention is not limited to the several embodiments herein disclosed as various changes may be made in the electrical and mechanical assemblies without departing from the spirit of my invention as set forth in the following claims.

I claim:

1. In a radio compass, an -angularly movable directional antenna, a motor with a pair of reversing field windings for rotating said antenna, a radio receiver Operating out of said antenna :and having an instrument relay in an output circuit thereof, said relay including a moving contact displaceable in opposite directions from its electrical zero to engage one or the other of two relatively fixed contacts in accordance with the direction of displacement of said directional antenna from a selected on-course position, said contacts being fiexible vibratory members, where- -by the integrated time of closure of the movable contact upon a relatively fixed contact varies progressively with the magnitude of the displacement of the directional antenna from a selected on-course position, a pair of grid glow tubes each having one of said motor windings in the output circuit thereof, and circuit means including said movable contact of said relay and the respective relatively fixed contacts for controlling conduction through the respective tubes to regulate the direction and the speed of operation of said motor.

2. A radio compass of the type including an .angularly movable loop antenna and a non-directional' antenna, means including a radio receiver connected to said antennae for producing a direct current that changes polarity when the loop antenna is displaced in opposite directions from a balance position with respect to a preselected radio transmtter and increases in magnitude with the displacement of the loop antenna, a motor for rotating said loop antenna, said motor having a pair of field windings for determining the direction of rotation of the motor, and control means for energizing said motor for operation at a speed that varies progressively with the departure of the loop antenna from on-course position with respect to a selected radio transmitter; characterized by the fact that said control means comprses a pair of grid glow tubes having said field Windings in their respective output circuits, and an instrument relay energized by the direct current from said current-producing means for selectively controlling conduction through said. tubes in accordance with the orentation of said loop antenna, said relay having a movable system for dsplacing a fiexble continuously vibrating contact :arm between a pair of relatively stationary and flexible `continuously Vibrating contacts, whereby the values of the time-integrated closures of said contact arm upon said contacts may progressively vary with the magnitude of the departure of the loop antenna from a selected on-course position.

ANTHONY H. LAMB. 

